Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$35.60	13.350%	$40.3526	$40.35	$40.35	$40.40
Purchase #2	$229.71	3.608%	$237.9979	$238.00	$238.00	$238.00
Purchase #3	$173.81	11.670%	$194.0936	$194.09	$194.10	$194.10
Purchase #4	$31.25	13.760%	$35.55	$35.55	$35.55	$35.60
Purchase #5	$41.60	12.407%	$46.7613	$46.76	$46.75	$46.80
Purchase #6	$189.86	13.247%	$215.0108	$215.01	$215.00	$215.00
Purchase #7	$38.86	4.799%	$40.7249	$40.72	$40.70	$40.70
7 purchase totals =	$740.69		$810.4911	$810.48	$810.45	$810.60